Vacuum variable condenser



April 3, 1956 J. E. JENNINGS ET AL 2,740,927

VACUUM VARIABLE CONDENSER Filed Dec. 51, 1952 LEW/S B. STEWARD 1% theirA TTORNE V United States Patent VACUUM VARIABLE CONDENSER Jo EmmettJennings and Lewis B. Steward, San Jose,

alifi, assignors, by mesne assignments, to Jennings Radio ManufacturingCorporation, San Jose, Calif., a corporation of California 7 ApplicationDecember 31, 1952, Serial No. 328,941

4 Claims. (Cl. 317-245) Our invention relates to vacuum variablecondensers; and one of the objects of the invention is the provision ofan improved mounting for the condenser plates characterized by a veryhigh degree of rigidity and strength.

Another object is the provision of a shorter and more compact condenserstructure, and one in which the stresses imposed by temperature changesand expansion difierentials, is less severe where metal and glass partsare united, as in the seals.

Another object is the provision of a condenser in which each set of theplates and its mounting structure are in immediate or very intimatemechanical and electrical contact, so that inductance in these portionsof the condenser is materially reduced.

Still another object of the invention is the provision of a vacuumcondenser having a glass envelope characterized by a fold-over sectionadjacent one of the metal terminals, so that the increased insulationthus afforded, together with the electrostatic field produced at theoutwardly extending feathered edge of the terminal sealed in the glass,enforces a higher surface flash-over voltage.

In addition to the above, our vacuum variable condenser has many otherobjects, some of which with the foregoing will be set forth at length inthe following description where that form of the invention which hasbeen selected for illustration in the drawing accompanying and forming apart of the present specification is explained. In said drawings, oneform of the invention is shown, but it is to be understood that it isnot limited to that form, since the invention as set forth in the claimsmay be embodied in a plurality of forms.

Referring to the drawings:

Fig. 1 is an elevation of our vacuum variable condenser, partly invertical compound section. The planes of section are indicated by theradial lines 11 of Fig. 3.

Fig. 2 is a fragmentary view in vertical half section, showing themounting of the plates. The scale is twice that of Fig. 1.

Fig. 3 is a plan view of the mounting plate for the fixed condenserplates.

Referring first to Fig. 1, the vacuumized shell or envelope of ourcondenser includes an end cap or terminal made of suitable gauge copperand comprising three main portions, concentrically arranged about themain long axis 2 of the condenser. The central or stud portion 3 of theterminal is an inwardly opening cup, very slightly tapered toward theouter end. This stud is engaged by a mounting clip or bracket when thecondenser is placed in a circuit. At its inner end the stud flaressharply into a radially extending flange 4, which turns backwardly,along but divergently from the center stud in the flange 6.

The outer edge of the flange 6 is feathered and united in a vacuum tightmetal-to-glass seal 7 with the folded over end 8 of the glass cylinder9, which forms a major part of the vacuumized envelope of our condenserstructure. At its opposite end, a similar metal-to-glass seal 12 joinsthe cylinder to the copper end cap 13.

integrally united to the terminal cap by brazing along the inner face ofthe radial flange portion 4, is a mounting plate 16, Fig. 3, from thecenter of which tongues 17 are struck upwardly to fit snugly into theflaring open end of the stud. The mounting plate is also provided with aconcentric annular head 13 snugly enclosing the annular corner fromwhich the flange 6 turns upwardly. This bead also plays an importantpart in stiffening the mounting plate.

In order to facilitate the application of brazing solder between themounting plate and the radial stud flange 4, the former is provided withholes 19; and in order to avoid an orphaned air pocket, the mountingplate is also formed with holes 21 in the annular bead 18.

In addition to the head 18, the mounting plate is further stitfenedagainst distortion and vibration by the inwardly turned peripheralflange 22, which also forms a secure and concentric seat for mountingthe unit assembly of fixed plates 23 of the condenser.

The condenser plates 23 are cylindrical shells arranged concentrically,each shell at one end being substantially U-shaped in axial section, andbeing sized to fit snugly around each successively smaller shell. Thisunit of as sembled shells is brazed together and to the mounting platewithin the peripheral flange, forming an exceedingly rigid structurewith a high degree of accuracy of concentric spacing about the long axisof the condenser.

The importance of concentric accuracy and of structural stability isvery great, since the interleaved movable plates 26 of the condenser,each with its reentrant flange 27, are also similarly concentricallydisposed and brazed together and within the raised flanged seat 28,formed on the periphery of the mounting plate 29, by which the movableplates 26 are mounted on the mobile end 31 of the bellows 32.

The plate 29 is formed with a concentric bead 33 on the side oppositethe peripheral seat; and this bead provides an accurate setting for theend of the bellows which is brazed to the plate. The flanged and beadedconstruction of the mounting plate not only provides an accuratemounting for the unit assembly of movable condenser plates, but byspacing the plate assembly close to the end of the bellows with supporton the peripheral flange, vibration and distortion are prevented, whileat the same time preserving a compact and rigid structure.

One or more holes 34 are made in the bead 33 to permit easy cleaning andprevent the trapping of reaction products and air in pockets that wouldprevent complete evacuation of the envelope.

Because of physical limitations in the drawing, the plates of thecondenser are necessarily shown with a degree of thickness and arespaced apart a considerable distance. Actually they are very thin andvery close together for reasons relating to the capacity of thecondenser; and unless great rigidity and a high degree of accuracy inmounting and in movement are attained, objectionable changes inelectrical characteristics and capacity of the instrument or evenshorting across the plates is inevitable.

The fixed end of the bellows is connected to the cap 13 to complete thevacuumized chamber in which the plates lie. This is done by extendingthe conical end 36 of the cap inwardly to a flange 37 in tightengagement with the end of the bellows sleeve extension 38, which snuglysurrounds the thickened end of the bearing tube 39. The three parts 37,38 and 39 are then brazed together at their juncture, as shown in Fig.1, thus providing a wide and vibration-free hearing or slideway for thecylindrical thick walled hollow stem 41, by which the movable plates 26are given their axial movement. The bearing tube and stem are preferablyof a copper alloy such as brass or bronze and are of substantialthickness as shown. These qualities and a stem diameter of abouttwo-fifths the diameter of the largest condenser plate 26, provides thelateral breadth of mounting needed to insure rigid stability and freedomfrom vibration.

The stem 41 is rigidly attached at its inner end to the mobile end 31 ofthe bellows, preferably by threading it into the annular flange .42concentrically disposed on the inside of the bellows end and brazedthereto. Closing the outer end of the cylindrical stem is the head 43,held in place by screws 44, the heads of which form stops to limit theinward travel of the stem and connected plates 26. The center of thehead is bored and threaded to receive in snug engagement the threadedoperating shaft 46, journaled for rotary but not axial movement in theend of the terminal 47, which has a peripheral edge 48 bearing againstthe conical end of the cap 13; and forms a hood around the exposed outerends of the stem 41 and bearing tube 39.

A knob 49 is fixed on the outer end of the operating shaft so that itcan be turned to adjust the movable plates 26. Atmospheric pressure isof course always exerted against the stem to force it inwardly, movingthe plates 26 into interleaved relation with the fixed plates. Thispressure is carried by a ball thrust bearing interposed between theshaft 46 and the terminal hood. Our condenser is connected in thecircuit in which it is to be used by clips or other suitable meansarranged to engage the cap 3 at one end and cap 13 at the opposite end.

An aperture 52 is made in the side of the hollow stem to permitinsertion of a stop pin, in the event it is necessary to renew the head43. With the pin in place, the f bellows is prevented from uncontrolledexpansion into the envelope with a resultant crushing together of theshells.

We claim:

1. In a vacuum condenser, an evacuated envelope hav- I 5 ing a metallicend wall comprising a central inwardly opening cup forming a terminalelectrode of the condenser, said cup having its peripheral edge foldedoutwardly and back to form a concentric return flange spaced outwardlyfrom the cup, a flat mounting plate integrally united to the folded overedge of the cup and having integral tongues extending into andintegrally united with the cup and having a concentric peripheral flangeon the face opposite the cup, a cylindrical condenser plate brazed tothe mounting plate within the flange, a plurality of successivelysmaller cylindrical condenser plates brazed to each other and to themounting plate, a glass shell forming part of the envelope and at oneend folded inwardly and back in a concentric return flange spacedinwardly from the shell, and a metal-to-glass sealed joint uniting theperipheral edges of the return flanges.

2. In a vacuum condenser, an evacuated envelope having a metallic endwall comprising a central inwardly opening cup forming a terminalelectrode of the condenser, said cup having its peripheral edge foldedoutwardly and back to form a concentric return flange spaced outwardlyfrom the cup, a flat mounting plate integrally united to the folded overedge of the cup and having a concentric bead embracing the return flangeand a peripheral concentric flange onthe side opposite the bead, anassembly of concentric cylindrical condenser plates integrally united tothe mounting plate within the flange, a glass shell forming part of theenvelope and at one end folded inwardly and back in a concentric returnflange spaced inwardly from the shell, and a metal-toglass sealed jointuniting the peripheral edges of the return flanges.

3. In a vacuum condenser, an evacuated envelope having a cylindricalmetallic end wall forming a terminal electrode of the condenser, ametallic. bellows having a closed inner end extending into the envelopeand with the cylindrical end wall closing the end of the envelope, aflat mounting plate having an outwardly extending concentric, annularbead within which the closed end of the bellows is integrally united tothe mounting plate, an annular flanged seat concentrically formed aroundthe periphery of the mounting plate on the side opposite the head, abearing tube extending into the envelope and continuous with thecylindrical endv wall, a stem slidably mounted in the bearing tube andfixed at its inner end to the closed end of the bellows, an assembly ofconcentric cylindrical condenser plates immediately adjacent themounting plate and integrally united thereto within the annular seat,and means for moving the stem in the bearing tube to vary the axialposition of the mounting plate within the envelope.

4. In a vacuum condenser, an evacuated envelope having a cylindricalmetallic end wall forming a terminal electrode of the condenser, ametallic bellows having a closed cylindrical inner end extending intothe envelope and with said cylindrical metallic end wall closing the endof the envelope, an annular mounting plate having an outer peripheralflanged seat and a central circular aperture within which aperture theclosed, cylindrical end of the bellows is integrally united, an assemblyof concentric cylindrical condenser plates fixed in said flanged seat,and means for varying the axial position of said annular mounting platewithin the envelope.

References Cited in the tile of this patent UNITED STATES PATENTS2,192,062 Hansell Feb. 27-, 1940 2,230,125 Usselman Jan. 28, 19412,339,663 Teare Ian. 18, 1944. 2,358,200 Atlee Sept. 12, 19.44..2,447,719 Sorg Aug. 24, 1948 2,451,557 Howes Oct. 19, 1948 2,511,338Jennings June 13, 1-950 2,556,846 Longacre June 12, 1951 2,558,357 GrimmJune 26, 195.1 2,575,726 Peck Nov. 20, 1951 FOREIGN PATENTS 589,728Great Britain 11111.6 27, 1947 638,857 Great Britain June 14, 1950

